Chapter 2. Important Changes to External Kernel Parameters

This chapter provides system administrators with a summary of significant changes in the kernel shipped with Red Hat Enterprise Linux 6.6. These changes include added or updated procfs entries, sysfs default values, boot parameters, kernel configuration options, or any noticeable behavior changes.
MemAvailable
Using this parameter provides an estimate of how much memory is available for starting new applications without swapping. However, unlike the data provided by the Cache or Free fields, MemAvailable takes into account page cache and also that not all reclaimable slab will be reclaimable due to items being in use.
overcommit_kbytes
This parameter allows the user to determine the specific number of kilobytes of physicial RAM that a committed address space is not permitted to exceed when the overcommit_memory parameter is set to "2". Therefore, overcommit_bytes works as the counterpart to the overcommit_ratio, and setting one automatically disables the other.
meminfo_legacy_layout
Setting this parameter to a non-zero value will disable the reporting of new entries introduced to /proc/meminfo and the kernel will keep the legacy (2.6.32) layout when reporting data through that interface. Note that the default value is "1". This parameter is available to Red Hat Enterprise Linux 6 only, for reasons of retroactive compatibility.
disable_cpu_apicid
This parameter allows the kdump kernel to disable BSP during boot and then to successfully boot up with multiple processors. This resolves the problem of lack of available interrupt vectors for systems with a high number of devices and ensures that kdump can now successfully capture a core dump on these systems.
earlyprintk
Previously usable only for VGA hardware, this parameter now supports the "efi" value, which allows users to debug early booting issues on EFI hardware.
edac_report
By setting the value of this parameter to "on" or "off", the user can enable or disable the Error Detection and Correction (EDAC) module to report hardware events. It is also possible to make EDAC impossible to be overridden by a higher-priority module by using the "force" value. The default value of this parameter is "on".
intel_iommu
This parameter enables the user to turn off the support of large pages, using the "sp_off" value. By default, however, large pages are supported as long as the Intel input/output management unit (IOMMU) meets the requirements.
nfs.recover_lost_locks
Previously, NFSv4 clients could resume expired or lost file locks. Nevertheless, this sometimes resulted in file corruption if the file was modified in the meantime. Therefore, recovering these locks has been disabled, but can be enabled by changing the value of the above parameter from "0" to "1". Note, however, that doing so still carries a risk of data corruption.